Spiral Groove SG2 turntable
Photograph: TONEAudio Magazine
The evolution of high-end turntables illustrates how such a perfect merger of art and science can be approached from either side. The Linn Sondek began as a simple design that, while compromised in some ways, was implemented so artfully that sonically it transcended its origins. The original idea behind the SOTA turntable, on the other hand, was to build "a better Linn" by correcting the Sondek's design flaws. The SOTA was a vastly superior design, and, like any self-respecting engineer, I bought one.
Unfortunately, the SOTA wasn't realized with the artistry that had made the Linn so special, and never quite delivered on its promise. The net result was a kind of toss-up between the art-based Linn and the engineering-based SOTA, with proponents of each claiming that their approach was better. The designs and performance of both evolved and were improved over the years, the Linn through more advanced engineering of its power supply and chassis, the SOTA through better execution of its design principles, and modifications that sometimes weren't well understood, even by the designer(s), but that resulted in better sound. And somewhere along in there, I replaced my early-model SOTA with a second- or third-generation SOTA Star.
Does a Spiral Groove begin at the inside or the outside?
Allen Perkins has been designing, improving, and redesigning turntables for over 20 years, and well understands the importance of both art and science. He played key roles in the evolution of the SOTA, first as a frustrated owner working on his own 'table, and later as one of the company's managers. One of those roles was to provide telephone support to customers, which exposed him to even more issues with the 'tables, as well as a universe of users' tweaks and modifications. When, eventually, he was put in a position to influence SOTA's designs, he incorporated what he'd learned into improved versions of the existing models and a new, vastly improved turntable model, the Cosmos.
A few years later Perkins left SOTA to form Immedia, his import and distribution firm. But he continued to design turntables. Some of the SOTA's design elements were incorporated in his new turntables, the Immedia RPM-1 and 2, but for the most part, the new designs were radically different from the SOTAs. One thing Perkins had noticed while developing the Cosmos was that prototype chassis sounded better naked than when hung on springs inside a box. Measurements convinced him that this was because the suspended versions were in constant motion. Ergo, the RPM models eschewed spring suspension and any sort of external box, and the theme of eliminating any spurious movement was applied throughout the designs.
The RPMs began a new design cycle for Perkins. He'd improved the engineering-based SOTA with empiricism and art, and taken it about as far as it could go with the Cosmos. The RPM 'tables were the start of a new line, one that combined what he'd learned from the SOTA's evolution with new, original elements, embodied in an entirely new design. As had the Linn, SOTA, and SOTA Star before it, an RPM combo of turntable and tonearm (footnote 1) served as my reference for a time.
Spiral Groove SG2
The Spiral Groove turntables look similar to the RPMs; as Allen Perkins noted in his interview in the January 2010 issue (p.59), "There are no new ideas in the Spiral Groove 'tables." They do include, however, several refinements that reflect a mix of evolution, new ideas, and more advanced design and production capabilities. The boxless chassis and dense, multilayer construction resemble those of the RPMs, but where the smaller RPMs had a three-layer chassis, the SG2 has five: two thin layers of damping material separating three aluminum plates. The Spiral Groove platters resemble the RPMs', but their structures are quite different. The SG2 platter has layers of aluminum, an impregnated phenolic, vinyl, and graphite; their placement, thicknesses, and even assembly order have been chosen to most effectively couple with the record and drain vibrations away.
For example, the SG2's bearing assembly alone incorporates a number of significant refinements. There are no bronze bushings or press-fit components, both sources of variability and, possibly, unwanted motion. Instead, hardened steel sleeves are used. These can be finished to very tight tolerances, allowing the contact surfaces to be minimized and placed optimally to eliminate any radial movement. Another change to the bearing assembly is that the magnet assemblies used to support the platter's weight have been changed and reoriented based on electromagnetic circuit models, to eliminate stray magnetic fields that might affect the cartridge. The SG2 even uses a different system of elastomer plugs to hang and isolate the motor subplate from the main chassis.
Footnote 1: Michael Fremer reviewed the RPM tonearm for Stereophile in May 1997; Wes Phillips reviewed the RPM turntable in September 1997. Ed.